Superconducting motor rotor and motor rotor low-temperature system

Abstract

The invention discloses a superconducting motor rotor and a motor rotor low-temperature system, the superconducting motor rotor comprises a peripheral frame, a support skeleton, a superconducting magnet and an intermediate shaft, a vacuum cavity is formed in the peripheral frame, the support skeleton is located in the vacuum cavity, the superconducting magnet is connected to the support skeleton, and the intermediate shaft is located on the inner side of the support skeleton and fixedly connected with the peripheral frame. The rotor structure of the superconducting motor is formed, the cooling assembly can cool the superconducting magnet by cooling the supporting framework, so that the rotor is in a low-temperature environment, the mounting cavity is formed in the intermediate shaft, the low-temperature assembly for cooling the rotor can be mounted in the mounting cavity, and the low-temperature assembly is mounted in the rotor, so that the temperature of the rotor is reduced. The occupied area of external low-temperature system components can be effectively reduced, the vacuum cavity formed in the peripheral frame can conduct heat insulation, and then a good low-temperature environment is created for the rotor.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting motors, and in particular to a superconducting motor rotor and a motor rotor cryogenic system. Background Art

[0002] A superconducting motor is an advanced motor that uses superconducting magnets for excitation. At low temperatures, the resistance of superconducting magnets is close to zero, and a very strong magnetic field can be generated in a limited space. Compared with conventional motors, superconducting motors have a higher torque density and have the advantages of small size, light weight, and high efficiency.

[0003] However, superconducting motors need to transmit low-temperature cooling to the superconducting magnets in the rotor through a low-temperature system to maintain the superconducting state of the superconducting magnets. For example, the low-temperature cooling system for high-temperature superconducting motor rotors with publication number CN109525069A transmits low-temperature neon gas to the inside of the rotor through a magnetic fluid sealing device to achieve low temperature inside the rotor.

[0004] In the prior art, the cryogenic system of a superconducting motor is generally arranged outside the superconducting motor, and the cryogenic refrigerant is transmitted to the rotor through a magnetic fluid rotary seal device. Since the cryogenic system requires a certain amount of floor space, the technical advantage of the superconducting motor over conventional motors is weakened. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, propose a superconducting motor rotor and a motor rotor cryogenic system, and solve the technical problem that the superconducting motor rotor cryogenic system in the prior art occupies a large area.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a superconducting motor rotor, comprising: The outer frame forms a vacuum chamber inside; A supporting frame is located in the vacuum chamber; A superconducting magnet connected to the support frame; and The intermediate shaft is located at the inner side of the supporting frame and is fixedly connected to the outer frame. An installation cavity is arranged inside the intermediate shaft, and the installation cavity is used for installing the cooling component.

[0007] In some embodiments, the inner side of the outer frame is connected to the intermediate shaft, a support frame is provided inside the mounting cavity, the support frame is provided with a mounting hole, the mounting hole is used for the installation of the cooling component, and the cooling component, the intermediate shaft and the outer frame are enclosed to form the vacuum cavity.

[0008] In a second aspect, the present invention further provides a motor rotor cryogenic system, comprising: The superconducting motor rotor; and A cooling component is installed in the installation cavity. The cooling component is connected to the support frame through a pipeline and is used to cool the support frame by inputting a low-temperature medium into the support frame.

[0009] In some embodiments, the cryogenic system further includes a medium supply unit, which is connected to the cooling component and is used to supply normal temperature medium to the cooling component and receive the normal temperature medium output by the cooling component.

[0010] In some embodiments, the cooling component includes a countercurrent heat exchanger and an expander. The expander is connected to the countercurrent heat exchanger and the supporting skeleton, and is used to receive the sub-low-temperature medium of the countercurrent heat exchanger and form a low-temperature medium, and transport the formed low-temperature medium to the supporting skeleton. The countercurrent heat exchanger is connected to the supporting skeleton and the medium supply unit, and is used to receive the normal temperature medium input by the medium supply unit and the low-temperature medium behind the supporting skeleton, and forms the sub-low-temperature medium through heat exchange between the low-temperature medium and the normal temperature medium.

[0011] In some embodiments, the medium supply unit includes a compressor, a cooler and a magnetic fluid seal, the magnetic fluid seal is connected to the intermediate shaft and to the countercurrent heat exchanger, the cooler is connected to the magnetic fluid seal, the compressor is connected to the cooler, and the compressor, the cooler, the magnetic fluid seal, the countercurrent heat exchanger, the expander and the supporting frame can provide medium circulation.

[0012] In some embodiments, the magnetic fluid seal includes a rotating shaft, a sleeve, a plurality of permanent magnets and a plurality of magnetic poles. The rotating shaft is fixedly connected to the intermediate shaft. The sleeve surrounds the circumferential direction of the rotating shaft and is rotatably connected to the rotating shaft. Each of the magnetic poles is installed on the inner side of the sleeve and forms a filling cavity filled with magnetic fluid between the sleeve and the rotating shaft. At least one medium input cavity and at least one medium output cavity are formed between the magnetic poles. The medium input cavity and the medium output cavity are used to input or output the medium, respectively. Each of the permanent magnets is installed between each of the magnetic poles, and the magnetic properties of adjacent permanent magnets are opposite.

[0013] In some embodiments, an input flow channel and an output flow channel are disposed inside the rotating shaft, and the output flow channel and the input flow channel are connected to the input interface and the output interface of the counterflow heat exchanger respectively.

[0014] In some embodiments, the magnetic fluid seal also includes a spacer ring, an input pipe and an output pipe, the spacer ring is installed in the medium input cavity and the medium output cavity, the input pipe and the output pipe pass through the spacer ring and are connected to the medium input cavity and the medium output cavity respectively.

[0015] In some embodiments, a slip ring and a carbon brush may be provided on the rotating shaft, a cable channel is provided on the inner side of the rotating shaft, the slip ring leads out the cable, and the cable is led out through the cable channel to provide the required power to the expander.

[0016] Compared with the prior art, the superconducting motor rotor provided by the present invention is provided with an outer frame, a supporting frame, a superconducting magnet and an intermediate shaft. A vacuum chamber is formed inside the outer frame, the supporting frame is located in the vacuum chamber, the superconducting magnet is connected to the supporting frame, and the intermediate shaft is located on the inner side of the supporting frame and fixedly connected to the outer frame to form the rotor structure of the superconducting motor. The cooling component can cool the superconducting magnet by cooling the supporting frame, thereby placing the rotor in a low-temperature environment. Since an installation cavity is provided inside the intermediate shaft, the installation cavity can be used for installing a low-temperature component of the cooling rotor. The low-temperature component can be installed inside the rotor to effectively reduce the footprint of external low-temperature system components. The vacuum chamber formed inside the outer frame can be insulated, thereby creating a good low-temperature environment for the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of a low-temperature system for a motor rotor provided in an embodiment of the present invention; Figure 2 It is a schematic structural diagram of a magnetic fluid seal provided in an embodiment of the present invention.

[0018] Reference numerals in the figures: 10—peripheral frame 11—vacuum chamber 20—support frame 12—support frame 13—iron core 22—magnet support frame 30—superconducting magnet 40—intermediate shaft 41—installation cavity 42—support frame 50—cooling component 51—counterflow heat exchanger 52—Expander 60—Medium supply unit 61—Compressor 62—Cooler 63—Magnetic fluid seal 631—Rotating shaft 632 - jacket 633 - permanent magnet 634 - magnetic pole 635—spacer ring 636—input pipe 637—output pipe 638—slip ring 639—carbon brush 6311—input flow channel 6312—Output channel 6313—Cable channel 6341—Media input cavity 6342—Media output cavity. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] In order to solve the technical problem in the prior art that the cryogenic system of a superconducting motor rotor occupies a large area, an embodiment of the invention provides a superconducting motor rotor and a motor rotor cryogenic system to reduce the area occupied by the motor rotor cryogenic system.

[0021] A superconducting motor rotor provided by an embodiment of the present invention, such as Figure 1 As shown, it includes an outer frame 10, a support skeleton 20, a superconducting magnet 30 and an intermediate shaft 40. A vacuum chamber 11 is formed inside the outer frame 10; the support skeleton 20 is located in the vacuum chamber 11; the superconducting magnet 30 is connected to the support skeleton 20; the intermediate shaft 40 is located on the inner side of the support skeleton 20 and is fixedly connected to the outer frame 10, and an installation cavity 41 is provided inside the intermediate shaft 40, and the installation cavity 41 is used for installing a cooling component 50 of the cooling support skeleton 20.

[0022] Specifically, the superconducting motor rotor is provided with an outer frame 10, a support skeleton 20, a superconducting magnet 30 and an intermediate shaft 40. A vacuum chamber 11 is formed inside the outer frame 10. The support skeleton 20 is located in the vacuum chamber 11. The superconducting magnet 30 is connected to the support skeleton 20. The intermediate shaft 40 is located on the inner side of the support skeleton 20 and is fixedly connected to the outer frame 10 to form the rotor structure of the superconducting motor. The cooling component 50 can cool the superconducting magnet 30 by cooling the support skeleton 20, thereby placing the rotor in a low-temperature environment. Since an installation cavity 41 is provided inside the intermediate shaft 40, the installation cavity 41 can be used for installing a low-temperature component of the cooling rotor. The low-temperature component can be installed inside the rotor to effectively reduce the footprint of external low-temperature system components. The vacuum chamber 11 formed inside the outer frame 10 can be insulated, thereby creating a good low-temperature environment for the rotor.

[0023] In this embodiment, the outer frame 10 includes a central hole cylinder and a sealing end plate structure fixed to both ends of the cylinder, and the intermediate shaft 40 passes through the sealing end plate and is fixedly connected to the sealing end plate.

[0024] In this embodiment, Figure 1As shown, the support skeleton 20 includes a support member and a magnet support frame 22, the inner side of the support member is fixed to the intermediate shaft 40, the magnet support frame 22 is fixed to the outer side of the support member, and the superconducting magnet 30 is fixed to the magnet support frame 22. A fluid channel is arranged inside the magnet support frame 22. When the low-temperature medium flows through the fluid channel, the magnet support frame 22 will be cooled, and then the superconducting magnet 30 will be cooled by heat exchange between the magnet support frame 22 and the superconducting magnet 30. Through the above arrangement, the vacuum chamber 11 can be formed inside the rotor, thereby avoiding the low-temperature system structure being too complicated and occupying a large space due to the arrangement of the vacuum chamber 11, and through the heat insulation of the vacuum chamber 11, only the magnet support frame 22 and the superconducting magnet 30 inside the rotor will be in a low-temperature environment, while components other than the magnet support frame 22 and the superconducting magnet 30 will be in a normal temperature environment.

[0025] In this embodiment, a heat insulating layer may be wrapped on the surface of components other than the magnet support frame 22 and the superconducting magnet 30 to ensure that the components other than the magnet support frame 22 and the superconducting magnet 30 maintain a room temperature.

[0026] In this example, a support frame 12 and an iron core 13 are also provided inside the outer frame 10. The support frame 12 is fixed to the intermediate shaft 40. The iron core 13 is fixed to the support frame 12 and is located on the inner side of the magnet support frame 22 and is separated from the magnet support frame 22. The support member and the magnet support frame 22 form a low-temperature environment through a low-temperature medium, and the iron core 13 forms a normal temperature environment through the separation from the magnet support frame 22.

[0027] In one embodiment, Figure 1 As shown, the inner side of the outer frame 10 is connected to the intermediate shaft 40, and a support frame 42 is provided inside the mounting cavity 41. The support frame 42 is provided with mounting holes, and the mounting holes are used for the installation of the cooling component 50, so that the cooling component 50, the intermediate shaft 40 and the outer frame 10 are surrounded to form a vacuum cavity 11. Specifically, the cooling component 50 can be installed and fastened to the support frame 42 through the mounting holes of the support frame 42, and a closed vacuum structure can be formed inside the intermediate shaft 40. Since the intermediate shaft 40 and the outer frame 10 are also a closed structure, the inner side of the entire rotor and the interior of the intermediate shaft 40 will form a communicating vacuum cavity.

[0028] In this embodiment, the sealing end plate of the outer frame 10 is fixed to the intermediate shaft 40 .

[0029] The embodiment of the present invention also provides a low temperature system for a motor rotor, such as Figure 1 As shown, it includes the superconducting motor rotor and the cooling component 50. The cooling component 50 is installed in the installation cavity 41. The cooling component 50 is connected to the support frame 20 through a pipeline, and is used to cool the support frame 20 by inputting a low-temperature medium into the support frame 20.

[0030] Specifically, the motor rotor low-temperature system can form the cooling component 50 inside the rotor by installing the cooling component 50 in the installation cavity 41. While providing a low-temperature environment for the superconducting magnet 30 of the rotor, it can also effectively reduce the space occupied by the low-temperature system and improve the compactness of the low-temperature system.

[0031] It can be understood that the cooling component 50 can be any cooling device that can pass low-temperature medium into the supporting frame 20.

[0032] In this embodiment, the medium is helium.

[0033] In one embodiment, Figure 1 As shown, the low temperature system further includes a medium supply unit 60, which is connected to the cooling assembly 50 and is used to supply normal temperature medium to the cooling assembly 50 and receive the normal temperature medium output by the cooling assembly 50. Specifically, the normal temperature medium is supplied to the cooling assembly 50 through the medium supply unit 60, and the normal temperature medium is cooled to a low temperature medium by the cooling assembly 50 and then passed into the support frame 20, thereby maintaining a low temperature environment of the support frame 20.

[0034] In this embodiment, the cooling component 50 cools the inside of the rotor, so that the low-temperature system does not need to be equipped with a cooling module outside the rotor to cool the normal temperature medium, thereby simplifying the structure of the rotor external medium supply unit 60 and reducing the footprint of the low-temperature system.

[0035] In one embodiment, Figure 1 As shown, the cooling component 50 includes a countercurrent heat exchanger 51 and an expander 52. The expander 52 is connected to the countercurrent heat exchanger 51 and the support frame 20, and is used to receive the sub-low-temperature medium of the countercurrent heat exchanger 51 and form a low-temperature medium, and transport the formed low-temperature medium to the support frame 20. The countercurrent heat exchanger 51 is connected to the support frame 20 and the medium supply unit 60, and is used to receive the normal temperature medium input by the medium supply unit 60 and the low-temperature medium behind the support frame 20, and to provide heat exchange between the low-temperature medium and the normal temperature medium, so that the normal temperature medium forms the said sub-low-temperature medium. Specifically, through the above arrangement, after the normal temperature medium is supplied into the counterflow heat exchanger 51 through the external medium supply unit 60, it will exchange heat with the low temperature medium inside the counterflow heat exchanger 51, form a sub-low temperature medium after cooling and pass into the expander 52, form a low temperature medium after expansion by the expander 52, and the low temperature medium is transported from the expander 52 to the support skeleton 20, and enters the counterflow heat exchanger 51 after heat exchange with the skeleton. The low temperature medium exchanges heat with the normal temperature medium supplied into the external medium supply unit 60 in the counterflow heat exchanger 51 to form a normal temperature medium, and then the formed normal temperature medium is output for subsequent reuse, thereby forming a low temperature medium for manufacturing a low temperature environment of the rotor.

[0036] In one embodiment, Figure 1 As shown, the medium supply unit 60 includes a compressor 61, a cooler 62 and a magnetic fluid seal 63. The magnetic fluid seal 63 is connected to the intermediate shaft 40 and to the countercurrent heat exchanger 51. The cooler 62 is connected to the magnetic fluid seal 63. The compressor 61 is connected to the cooler 62. The compressor 61, the cooler 62, the magnetic fluid seal 63, the countercurrent heat exchanger 51, the expander 52 and the support frame 20 can provide medium circulation.

[0037] In this embodiment, the compressor 61 can be a multi-stage turbine compressor. The helium at the outlet of each stage of the turbine compressor is first cooled by the cooler 62 before entering the next stage of the turbine compressor. The compressor 61 can also be other types of compressors such as a screw compressor.

[0038] Specifically, the medium supply unit 60 is configured as above. In the process of forming a low-temperature environment for the rotor, the high-pressure helium compressed by the compressor 61 is transmitted to the cooler 62 through a pipeline. After cooling, it is transmitted to the refrigerant transmission rotating coupling through a pipeline. After being converted from static to rotation, it is transmitted to the countercurrent heat exchanger 51 of the rotor intermediate shaft 40. After being cooled by the countercurrent heat exchanger 51, it is expanded by the expander 52 to perform work externally to form low-temperature helium. The low-temperature helium is then transmitted to the internal channel of the magnet support frame 22 through a pipeline. The magnet support frame 22 is cooled by convection. The magnet support frame 22 cools the superconducting magnet 30 by conduction. After passing through the magnet support frame 22, it enters the countercurrent heat exchanger 51 through a pipeline, exchanges heat with the helium entering from the rotor rotating coupling, and returns to room temperature to form room-temperature helium. The room-temperature helium is then converted from rotation to static by the refrigerant transmission rotating coupling and returned to the suction port of the compressor 61. In this way, a medium circulation is formed, and the medium creates a low-temperature environment for the rotor under the action of this circulation.

[0039] In one embodiment, Figure 2 As shown, the magnetic fluid seal 63 includes a rotating shaft 631, a sleeve 632, a plurality of permanent magnets 633 and a plurality of magnetic poles 634. The rotating shaft 631 is fixedly connected to the intermediate shaft 40. The sleeve 632 surrounds the rotating shaft 631 in a circumferential direction and is rotatably connected to the rotating shaft 631. Each magnetic pole 634 is installed on the inner side of the sleeve 632 and forms a filling cavity filled with magnetic fluid between the sleeve 632 and the rotating shaft 631. At least one medium input cavity 6341 and at least one medium output cavity 6342 are formed between the magnetic poles 634. The medium input cavity 6341 and the medium output cavity 6342 are respectively used for inputting or outputting medium. Each permanent magnet 633 is respectively installed between each magnetic pole 634, and the magnetism of adjacent permanent magnets 633 is opposite.

[0040] Specifically, the rotating shaft 631, the outer sleeve 632, a plurality of permanent magnets 633 and a plurality of magnetic poles 634 form a magnetic fluid rotating seal. The medium input chamber 6341 and the medium output chamber 6342 can be filled with medium. The medium input chamber 6341 is connected to the counterflow heat exchanger 51 and the cooler 62, so that the normal temperature medium can be input to the counterflow heat exchanger 51. The medium output chamber 6342 is connected to the counterflow heat exchanger 51 and the compressor 61, so that the normal temperature medium output by the counterflow heat exchanger 51 can be received, and the normal temperature medium can be returned to the compressor 61.

[0041] In this embodiment, Figure 2 As shown, the medium input cavity 6341 and the medium output cavity 6342 are each set as one.

[0042] In this embodiment, Figure 2 As shown, the magnetic pole 634 has teeth and grooves and a groove body for installing an O-ring, and the magnetic fluid is filled between the teeth and the rotating shaft 631.

[0043] In one embodiment, Figure 2 As shown, the interior of the rotating shaft 631 is provided with an input flow channel 6311 and an output flow channel 6312, and the output flow channel 6312 and the input flow channel 6311 are respectively connected to the input interface and the output interface of the counterflow heat exchanger 51. Specifically, by forming the input flow channel 6311 and the output flow channel 6312 inside the rotating shaft 631, it is convenient to input the medium from the magnetic fluid seal 63 to the counterflow heat exchanger 51, and conveniently to input the medium from the counterflow heat exchanger 51 back to the magnetic fluid seal 63, so that the medium is always inside the magnetic fluid seal 63, avoiding leakage of the medium, and simplifying the structure of the medium delivery pipeline.

[0044] In one embodiment, Figure 2 As shown, the magnetic fluid seal 63 further includes a spacer ring 635, an input pipe 636 and an output pipe 637. The spacer ring 635 is installed in the medium input cavity 6341 and the medium output cavity 6342. The input pipe 636 and the output pipe 637 pass through the spacer ring 635 and are respectively connected to the medium input cavity 6341 and the medium output cavity 6342. Specifically, the input pipe 636 and the output pipe 637 can respectively supply the medium to the input cavity 6341 and output from the medium output cavity 6342, and the spacer ring 635 can seal the input pipe 636 and the output pipe 637 to prevent leakage of the medium.

[0045] In this embodiment, the input pipe 636 is a high-pressure pipe, and the output pipe 637 is a low-pressure pipe.

[0046] In one embodiment, Figure 2As shown, a slip ring 638 and a carbon brush 639 may be provided on the rotating shaft 631, and a cable channel 6313 is provided inside the rotating shaft 631. The slip ring 638 leads out the cable, and the cable is led out through the cable channel 6313 to provide the required power to the expander 52 and the compressor 61. Specifically, the slip ring 638 and the carbon brush 639 can provide power for the expander 52, so that the cryogenic system can use its own power supply to provide a low-temperature environment for the rotor, without the need to set up a separate power supply device, thereby simplifying the structure of the cryogenic system, and the cable channel 6313 can protect the cable and prevent the cable from being exposed.

[0047] In order to better understand the present invention, the following Figure 1 to Figure 2 The technical solution of the present invention is described in detail: in the process of forming a low-temperature environment for the rotor, the high-pressure helium compressed by the compressor 61 is transmitted to the cooler 62 through a pipeline, and after cooling, it is transmitted to the medium input chamber 6341 of the refrigerant transmission rotating coupling through the helium input pipe 636, and after the static to rotation conversion, it is output through the output flow channel 6312 and transmitted to the countercurrent heat exchanger 51 of the rotor intermediate shaft 40, and after being cooled by the countercurrent heat exchanger 51, it is expanded by the expander 52 to perform work externally to form low-temperature helium, and the low-temperature helium is then transmitted to the internal channel of the magnet support frame 22 through a pipeline. The magnet support frame 12 is cooled by convection, and the magnet support frame 12 cools the superconducting magnet 30 by conduction. After passing through the magnet support frame 12, it enters the countercurrent heat exchanger 51 through a pipeline, exchanges heat with the helium entering from the rotor rotating coupling, and returns to room temperature to form room-temperature helium. The room-temperature helium is then input into the input channel through the countercurrent heat exchanger 51, and then enters the medium output cavity 6342. After being rotated to a stationary state by the refrigerant transmission rotating coupling, it returns to the suction port of the compressor 61 through the output pipe 637, thus forming a medium circulation, thereby creating a low-temperature environment for the rotor.

[0048] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A superconducting motor rotor, characterized in that: include: The outer frame forms a vacuum chamber inside; A supporting frame is located in the vacuum chamber; A superconducting magnet connected to the support frame; and The intermediate shaft is located at the inner side of the supporting frame and is fixedly connected to the outer frame. An installation cavity is arranged inside the intermediate shaft, and the installation cavity is used for installing the cooling component.

2. The superconducting motor rotor according to claim 1, characterized in that: The inner side of the outer frame is connected to the intermediate shaft, a support frame is provided inside the installation cavity, the support frame is provided with a mounting hole, the mounting hole is used for the installation of the cooling component, and the cooling component, the intermediate shaft and the outer frame are enclosed to form the vacuum cavity.

3. A low temperature system for a motor rotor, characterized in that: include: The superconducting motor rotor according to any one of claims 1 to 2; and A cooling component is installed in the installation cavity. The cooling component is connected to the support frame through a pipeline and is used to cool the support frame by inputting a low-temperature medium into the support frame.

4. The motor rotor cryogenic system according to claim 3, characterized in that: The low temperature system also includes a medium supply unit, which is connected to the cooling component and is used to supply normal temperature medium to the cooling component and receive the normal temperature medium output by the cooling component.

5. The motor rotor cryogenic system according to claim 4, characterized in that: The cooling component includes a countercurrent heat exchanger and an expander. The expander is connected to the countercurrent heat exchanger and the supporting frame, and is used to receive the sub-low-temperature medium of the countercurrent heat exchanger and form a low-temperature medium, and transport the formed low-temperature medium to the supporting frame. The countercurrent heat exchanger is connected to the supporting frame and the medium supply unit, and is used to receive the normal temperature medium input by the medium supply unit and the low-temperature medium behind the supporting frame, and forms the sub-low-temperature medium through heat exchange between the low-temperature medium and the normal temperature medium.

6. The motor rotor cryogenic system according to claim 5, characterized in that: The medium supply unit includes a compressor, a cooler and a magnetic fluid seal, the magnetic fluid seal is connected to the intermediate shaft and to the countercurrent heat exchanger, the cooler is connected to the magnetic fluid seal, the compressor is connected to the cooler, and the compressor, the cooler, the magnetic fluid seal, the countercurrent heat exchanger, the expander and the supporting frame can provide medium circulation.

7. The motor rotor cryogenic system according to claim 6, characterized in that: The magnetic fluid seal comprises a rotating shaft, an outer sleeve, a plurality of permanent magnets and a plurality of magnetic poles. The rotating shaft is fixedly connected to the intermediate shaft. The outer sleeve encloses the circumferential direction of the rotating shaft and is rotatably connected to the rotating shaft. Each magnetic pole is installed on the inner side of the outer sleeve and forms a filling cavity filled with magnetic fluid between the outer sleeve and the rotating shaft. At least one medium input cavity and at least one medium output cavity are formed between the magnetic poles. The medium input cavity and the medium output cavity are respectively used for inputting or outputting medium. Each permanent magnet is respectively installed between each magnetic pole, and the magnetism of adjacent permanent magnets is opposite.

8. The motor rotor cryogenic system according to claim 7, characterized in that: An input flow channel and an output flow channel are arranged inside the rotating shaft, and the output flow channel and the input flow channel are respectively connected to the input interface and the output interface of the counterflow heat exchanger.

9. The motor rotor cryogenic system according to claim 7, characterized in that: The magnetic fluid seal also includes a spacer ring, an input pipe and an output pipe. The spacer ring is installed in the medium input cavity and the medium output cavity. The input pipe and the output pipe pass through the spacer ring and are connected to the medium input cavity and the medium output cavity respectively.

10. The motor rotor cryogenic system according to claim 7, characterized in that: A slip ring and a carbon brush may be arranged on the rotating shaft, a cable channel is arranged inside the rotating shaft, the slip ring leads out a cable, and the cable is led out through the cable channel to provide the required power to the expander.

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